In seismic exploration, whether on land, at sea, or in a transition zone, large numbers of sensors are coupled together in groups to receive an acoustic signal and send a signal to a central receiver for detection. This signal is representative of geological structures which are analyzed for the likelihood of bearing hydrocarbons.
The presentation of such geological structures with adequate clarity and resolution requires large quantities of data. This data must be acquired over a long seismic cable or marine seismic streamer and conducted back to the central receiver. Current systems use optical fibers to carry the vast quantities of data due to the relatively large bandwidth of fiber optics and their relative immunity to many kinds of electromagnetic interference.
One of the weak links in the system just described is the portion which senses the acoustic signal and develops a signal for transmission to the central receiver. Recent developments have focused on fiber-optic sensors, so that the acoustic signal itself is used as the modulation means, creating a time varying effect on the optical path length of an optical fiber under the influence of the acoustic signal. These systems have proved to be effective, but technical developments remain before they reach large scale manufacture. In the meantime, there remains a need for some means to use the electrical signal from a conventional sensor, such as a hydrophone or a geophone, which may be a single or multiple axis geophone, or a combination hydrophone and a plurality of geophones, and convert that electrical signal into a useful optical signal for transmission to the central receiver and/or a recording medium.